1. Field of the Invention
The present invention relates to an insulating film forming composition and a production method of an insulating film. More specifically, the present invention relates to an insulating film forming composition for use as an interlayer insulating film material in a semi-conductor device or the like, which can form a film coating having an appropriate uniform thickness and moreover is useful for the formation of an insulating film excellent in dielectric characteristics and the like, and a production method of an insulating film.
2. Description of the Related Art
Conventionally, a silica (SiO2) film formed by a vacuum process such as vapor growth (CVD) method is often used as an interlayer insulating film in a semiconductor device or the like. In recent years, a coating-type insulating film mainly comprising a hydrolysate of tetraalkoxysilane, called SOG (spin-on-glass) film, comes to be used for the purpose of forming a more uniform interlayer insulating film. Also, with an increase in the integration of a semiconductor device and the like, a low-dielectric-constant interlayer insulating film mainly comprising a polyorganosiloxane, called organic SOG, is being developed.
However, the dielectric constant is about 4 even in the case of a CVD-SiO2 film exhibiting a lowest dielectric constant out of inorganic material films. The relative dielectric constant of an SiOF film which is being recently studied as a low-dielectric-constant CVD film is from about 3.3 to 3.5, but this film is highly hygroscopic and has a problem that the dielectric constant rises in the course of usage.
Under these circumstances, as regards the insulating film material excellent in the insulting property, heat resistance and durability, there is known a method of adding a high boiling point solvent or a thermally decomposable compound to organopolysiloxane to form pores, thereby decreasing the dielectric constant. However, even if the dielectric characteristics are decreased by forming pores, the porous film is disadvantageous, for example, in that the mechanical strength deteriorates and an increase of the dielectric constant occurs due to moisture absorption. Also, formation of pores connected with each other brings about a problem, for example, that copper used for wiring diffuses into the insulating film.
On the other hand, there is also known an attempt to obtain a film having a low refractive index and a low density by coating a solution where a low molecular cage-type compound is added to an organic polymer (see, JP-A-2000-334881 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). However, in this method, the effect of decreasing the refractive index and dielectric constant is insufficient.